Plastic Cell Filled Concrete

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Plastic cell filled concrete is a pavement built by stretching a thin plastic cell formwork over a compacted sub-base, filling the cells with concrete and compacting it. The result is a layer of small, interlocked concrete blocks that behaves as a flexible concrete pavement. Ocean Geosynthetics manufactures and supplies the plastic cell formwork in HDPE and LDPE (Ocean Plastic Cell Filled Concrete and LDPE Plastic Cell Filled Concrete) for rural roads, footpaths, yards and overlays.

What is plastic cell filled concrete?

Cell-filled concrete pavement (CFCP) was developed for low-volume roads where overloaded vehicles, poor drainage and waterlogging break up bituminous surfaces quickly. A framework of HDPE or LDPE cells, roughly square in plan when tensioned, is laid on a compacted subgrade or sub-base and filled with concrete, either roller-compacted (dry, low-slump) concrete or conventional concrete compacted with vibrators. For lighter duties the cells can be filled with stone.

In published Indian and Asian Development Bank descriptions, cells are typically about 150 mm × 150 mm with a depth of 100 to 150 mm, and the plastic is a thin sheet, around 0.2 to 0.5 mm. That makes the formwork very different from an HDPE geocell, whose 1.5 mm walls confine soil or aggregate as a structural layer.

How it works

The plastic walls divide the concrete into individual blocks and act as pre-formed joints. Shrinkage and thermal movement are taken up at the cell walls, so the slab does not need sawn expansion or contraction joints and does not develop random cracks across the surface. Under load, the blocks interlock and spread the load to the sub-base while the pavement as a whole can follow small settlements of the ground below, which is why it is described as a flexible concrete pavement.

Cell-filled pavement construction procedure

Build the embankment, subgrade and sub-base to the road specifications.
Provide camber suitable for rural roads. In high-rainfall areas (annual rainfall over 1000 mm), install a drainage layer as required by the Rural Roads Manual.
Set stone or concrete blocks, or bricks on end, along both edges of the carriageway, projecting 50 to 100 mm above the subgrade or sub-base, to contain and protect the cell-filled concrete.
Provide a firm shoulder with adequate drainage, roughly 0.85 m wide on each side. Vehicles running close to the edge can otherwise damage the unconfined blocks.
Stretch the plastic cell formwork over the compacted sub-base and tension it with iron spikes so the cells are close to square in plan.
Run nylon threads 10 mm below the top of the cells to stop the cells collapsing while they are filled.
If any cell stitches open during tensioning, staple them near the top, middle and bottom.
Fill the cells with loose concrete to a depth of 120 mm, about 20 mm above the cell depth, to allow for compaction.
Remove the iron spikes once the cells are filled. For roller-compacted concrete, two passes in static mode, two in vibratory mode and a final static pass normally give adequate compaction and a decent finish. The number of passes depends on aggregate texture and moisture content.
Conventional concrete with a slump of 30 to 40 mm can be compacted with pan vibrators instead.
Use a trial run to fix the number of roller passes, the vibration amplitude, the loose depth of concrete in the cells and the water content.
Cure the surface. In hot weather, cover it with moist jute mats or paddy straw to stop the concrete drying out.

Advantages of cell filled concrete pavements

No joint maintenance: the cell walls replace expansion and contraction joints, so there are no joints to seal.
Lower construction cost than conventional cement concrete pavement, and less concrete per square metre because the layer is thinner.
Easy repair: a failed block can be broken out and replaced with little effort and at low cost.
Recycled plastic can be used for the cell formwork.
Labour-based construction: the method needs little heavy equipment, so it suits remote sites and rural road programmes that aim to create local employment.
Resists rutting and waterlogging better than thin bituminous surfacing on low-volume roads, with low maintenance.
Quick to deploy: the formwork is light and compact to transport.

Function: base stabilisation, road surfacing and erosion protection on embankments. Sector: road construction.

Applications

Rural and village roads, especially in areas with waterlogging or poor drainage
Overlays on damaged bituminous (tar) roads
Footpaths and housing complex roads
Container yards and heavy vehicle parking areas
Haul roads for transporting mineral products
Road surface, shoulder and base stabilisation
Canal linings and embankment slope protection

Ocean Plastic Cell Filled Concrete / LDPE Plastic Cell Filled Concrete

Ocean supplies the cell formwork for pavements, roads, canals and embankments. LDPE Plastic Cell Filled Concrete uses low-density polyethylene, which is flexible and light, so the formwork stretches out easily on site and conforms to the sub-base. Tell us the carriageway width, length and pavement thickness and we will advise on cell size and quantity. For soil and aggregate confinement rather than concrete paving, see geocells; for separation under the sub-base on soft ground, see geotextiles.

Frequently asked questions

Is cell filled concrete a rigid or flexible pavement?

It is built from concrete but behaves between the two: each block is rigid, while the jointed layer of blocks can follow small movements of the ground, so it is often called a flexible concrete pavement.

How deep are the cells?

The procedure above uses cells about 100 mm deep, filled with 120 mm of loose concrete that compacts down to the cell height. Depths of 100 to 150 mm are common.

Does the pavement crack?

Movement is concentrated at the cell walls, which act as joints, so random surface cracking is avoided. Individual blocks can still fail under overload and are replaced one by one.